1. Field of the Invention
The present invention generally relates to (1) sheet folding devices whereby a sheet stack is accumulated, arranged, and folded; (2) sheet processors which are provided to image forming devices, such as copiers, printers, or printing machines, in a body or separately, and whereby predetermined processes such as classification processes, stacking processes, binding processes, and center-binding bookbinding processes are performed on the sheets (recording media) where the images are formed so that the sheets are discharged; and (3) image forming systems having the sheet processors and the image forming devices.
2. Description of the Related Art
There is extensively used a post-treatment device arranged at the downstream side of an image outputting device, such as a copier or printer, for, e.g., binding sheets driven out of the image forming apparatus. Today, even a post-treatment device with multiple advanced functions including an edge function and a center binding function is available. In addition, recently it is desired for the device to accomplish space-saving, cost-saving, and high productivity.
Conventionally, in this kind of sheet post-treatment device, the following method is applied as a method for folding for center binding bookbinding. That is, the center of the sheet stack is bound and the sheet stack is passed to a side of a folding roller couple exposed to a conveying path. The sheet stack is positioned and piled up at a folding position. A binding part of the sheet stack is pushed in a substantially perpendicular direction by a folding plate. The sheet stack is passed through the folding roller couple provided in a moving direction of the sheet stack so that the sheet stack is folded at the center. At this time, when a head end of the sheet stack passes the side of the folding roller couple exposed to a conveying path, the sheet stack comes in contact with the folding roller so that the end of the sheet may become folded and a jammed paper condition may occur. In order to avoid this, various methods are applied. For example, the folding roller is positioned to be greatly separated from the path or covered with sheet metal.
However, according to the above mentioned method, the distance between the nip position of the folding rollers and the folding plate, being out at a side of a direction facing the path, is long. Because of this, the moving distance of the folding plate increases and therefore a space for arranging a driving part of the folding plate becomes large and a large space is required. Furthermore, since the time for moving the folding plate increases, not only does the device size become large but also productivity of the machine becomes low. In order to solve this problem, there is an invention disclosed in Japanese Laid-Open Patent Application No. 2001-72328.
In this related art, while the folding roller is covered during time that the sheet stack is conveyed, the sheet stack is guided by a certain mechanism. Also, when the sheet stack is folded, the mechanism is moved out so that the folding roller is exposed.
However, in the above mentioned related art, although a small space may be required, the mechanism for moving out is required and so that the cost increases.